Overview
- The World Health Organization reports the H3N2 subclade K is rapidly spreading and predominating in parts of the Northern Hemisphere after early, heavy outbreaks in the United Kingdom, Japan, and Canada.
- CDC surveillance shows U.S. flu activity remains low but is rising with H3N2 dominant, and early analyses indicate about half of tested H3N2 viruses are subclade K, though recent reporting gaps cloud the full picture.
- Because vaccine strains were selected before subclade K emerged, protection against infection may be reduced, yet preliminary UK estimates show roughly 70–75% protection against pediatric hospitalization and about 30–40% in adults.
- U.S. flu vaccination uptake is lagging, with retail pharmacies administering about 2 million fewer shots from August through October compared with last year, prompting renewed calls for vaccination and basic prevention measures.
- Experts note H3N2 seasons often bring more severe illness, and clinicians urge early testing and timely antiviral treatment within 48 hours for those who become ill.